The coherence time of a light source is a well known property that describes the nature of the photon wavepackets. One of the primary reasons coherence time is important is to enable high visibility two-photon interference. The applications of this technique with quantum dot photon sources include optical quantum computing and quantum repeaters for quantum key distribution.
Currently, the standard approach to improve coherence times in quantum dots is to do one or both of the following things. First, the amount of charge created outside the quantum dot can be reduced by exciting preferably fully resonantly, or otherwise quasi-resonantly with the quantum dot. Second, optical cavity designs such as micropillars and photonic crystals may be employed to confine the optical mode to a small volume in the vicinity of the quantum dot, thus enhancing the radiative rate via the Purcell effect. In this case, the photon is radiated over a shorter period of time, giving the local electric field less time to fluctuate, and increasing the coherence time to lifetime ratio which improves two-photon-interference.